The Robustness of Pressure‐Driven Asthenospheric Flow in Mantle Convection Models With Plate‐Like Behavior

• Published in: Geophysical research letters 2020-09, Vol.47 (17), p.n/a
• Main Authors: Semple, Alana, Lenardic, Adrian
• Format: Article
• Language: English
• Subjects: anisotropy; Aquatic reptiles; Asthenosphere; Convection; Convection models; Direction; driving forces; dynamics; Earth mantle; Earth motion; Flow; Initial conditions; lithosphere; Mantle convection; Plate margins; Plate tectonics; Plates (tectonics); Pressure; Seismic activity; Seismic response; Tectonics; Upper mantle
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2020GL089556

Recent seismic observations challenge the conventional view that tectonic plates are driven by slab pull and ridge push forces. The observations indicate that the asthenosphere flows faster and in a different direction than the plate above. Previous mantle convection models argued that pressure‐driven flow, in combination with a non‐Newtonian upper mantle, can account for these observations. We expand those models by introducing a formulation that allows for the development of weak plate margins. Weak plate margins lead to an increase in the ratio of slab‐driven to pressure‐driven asthenosphere flow, but pressure‐driven flow remains active and increases with plate margin strength. Locally, the asthenosphere can drive plates and can change flow direction with depth. Furthermore, a non‐Newtonian upper mantle allows for a hysteresis effect where, depending on initial conditions, single‐plate and plate tectonic modes can exist at the same parameter conditions. Plain Language Summary It is generally thought that tectonic plates drive motion in the Earth's rocky interior. Recent observations have challenged this view as they indicate that interior motion can drive tectonic plates. Models of coupled tectonics and interior flow are used to address this discrepancy. The models reveal that the question of “does plate tectonics drive interior flow or does interior flow drive plate tectonics” may be ill founded as both possibilities may be active at the same time. The balance between the two drivers is found to depend on plate margin strength. The models also reveal that different tectonic modes can exist under the same physical conditions. This indicates a planet's initial state can determine if it will or will not have plate tectonics. Key Points Asthenosphere flow velocities can exceed tectonic plate velocity Asthenosphere flow can rotate with depth away from plate flow directions Hysteresis exists between plate tectonic and stagnant lid modes of mantle convection